This invention relates to a system for the jarring of tools which are stuck in places, such as an oil well and the like, and which provides for the use of ball bearing and double raceway arrangements including a hump element contained in one of the raceways while the other raceway is free of hump elements. More particularly, the invention relates to an adjustment device for the ball bearing arrangement for adjustment of the bearing arrangement following along the raceway cut in a mandrel. The raceway is inlaid and coated with "Tuborium" or other hard metal finish or coating to provide for incurring minimum wear. In each raceway there is a high point or hump element which takes a various amount of pull for the bearing to jump over and this may be set at a desired pull by increasing the pressure on the bearing with an Allen set screw or screws and similarly by decreasing the pressure by loosening of the screws. The tool force is released for hammer-down action. The bearing element does not follow the high point or hump element raceway in resetting, but follows a free raceway of the double track raceway for downward jarring.